Electron beam production system for electronic discharge



D. VITZTHUM Oct. 21, 1969 ELECTRON BEAM PRODUCTION SYSTEM FOR ELECTRONICDISCHARGE Filed Dec. 14, 1966 ATTYS.

US. Cl. 313-337 6 Claims ABSTRACT OF THE DISCLOSURE An electron beamproduction system with heating of the main cathode, constructed as adispenser cathode but not including a supply of emission substance orstorage chamber therefor, by electron bombardment from an auxiliarycathode likewise constructed as a dispenser cathode.

The invention relates to an electron production system for electronicdischarge vessels, in particular to an electron beam production systemfor HF power tubes, in which system a main cathode is provided at theend of an United States Patent G auxiliary electron discharge space, asan operating electrode, for the heating thereof through electronbombardment.

It is of particular importance for high power tubes operating with anelectron beam, in tubes of such type, for example, traveling wave tubeswith high power, an important difficulty resides in the necessity ofmaintaining the electrode which is required for the beam formation andwhich is immediately adjacent to the cathode sufficiently cool that itdoes not deliver any thermal emission when emission-promoting substancesare vapor-deposited thereon. This requires a cathode with as low afilament power as possible, heretofore sought to be obtained, at therespective operating temperature by eifecting certain measures such asthe utilization of a small volume for the reduction of the 'heatcapacity, and of a small surface area for the reduction of the heatconduction, as well as by the utilization of a supporting structure oflight weight and poor thermal conductivity for the reduction of thedissipation of heat.

It has already been proposed to heat the beam or main cathode of such anelectron production system by cathodic bombardment from an auxiliarycathode disposed in an auxiliary electron discharge space and in thiscase to construct at least the main cathode as a dispenser cathode, inparticular as an MK cathode.

The invention is directed to the reduction of the heat capacity of adispenser cathode disposed at the end of an auxiliary electron dischargespace and heated by cathodic bombardment by means of a specialconstructional arrangement to effect an increase in its heat economy.

In an electron beam production system of the type initially described,according to the invention this is achieved by the feature that there isprovided a main dispenser cathode, in particular an MK (metal capillary)cathode, which does not possess its own storage chamber and supply, andthe porous carrier disk for the emission substance which normally wouldclose the chamber, receives its emission promoting substance as a basicpart of the auxiliary cathode arranged therebehind and constructed as adispenser cathode, in particular as an MK cathode, and its filamentenergy as a working electrode of the auxiliary discharge system.

Through extensive tests it has been ascertained that the quantity ofemission promoting substance migrating from a normal capillary metalcathode towards the emis- 3,474,281 Patented Oct. 21, 1969 sion sideduring operation, i.e., the evaporation rate of, for example, barium, 1scompletely sufiicient to activate a further porous emission substancecarrier disk disposed in front of it, and which may even be larger, to asufficient degree, for the emission function and to maintain it capableof emission during operation, in which arrangement, in contrast toheretofore existing concepts, it is not even necessary to construct thisbasic main cathode in such a manner that the pores of the emission diskare its largest openings.

In a practical example, the supporting cylinder of this sheet materialor foil for the main cathode is so connected with the mounting enclosurefor the auxiliary cathode by an insulating part to form a semi-closedcontainer, that the two porous carrier disks for the emission substanceof the two capillary metal cathodes approximately form the end closuresof such space.

In this case the two mounting or supporting cylinders are especiallyadvantageously constructed and arranged in such a manner and providedwith such potentials that the occurring cathode bombardment achieves auniform predetermined heating of the porous emission substance carrierdisk of the main cathode.

One of the two mounting members or enclosures, or a further additionalcylinder of thin sheet material coaxial to such member may also includean aperture diaphragm and parallel thereto, an apertured partitioncorresponding to a Wehnelt electrode may also be provided, by means ofwhich the flow of electrons for the electron bombardment on the emissionsubstance carrier of the main cathode may be regulated with respect tothe cross section of the electron beam as well as with respect to theintensity, to permit a better adjustment of the desired operatingtemperature,

In especially advantageous manner, among other things in view of thetechnical arrangement, the porous emission substance carrier diskforming the main cathode may be mounted in such a manner that nocompletely closed space is formed between it and the following auxiliarycathode. The pores of the emission substance carrier disk in this casedo not necessarily form the largest openings in the space existingbetween the two porous disks.

Since the height of the required operating temperature is essentiallydeterminative for the filament power to be employed, an additional metallayer, for example out of a light or heavy platinum metal, may beapplied as an emission base or surface upon the porous body, for exampleof tungsten, for the lowering of the temperature on the basis of areduction of the electron atfinity.

Additional details of the invention will be explained in connection withthe form of construction illustrated purely schematically in thedrawing, which represents a longitudinal section of such a cathodesystem, in which parts which do not absolutely contribute to anunderstanding of the invention have been omitted or have not beendesignated.

The reference numeral 1 designates a carrier disk for an emissionsubstance, having a relatively large surface which is represented, so tospeak, as a basic part of a dispenser cathode, in particular an MKcathode, forming the main or beam cathode thereof. Such cathodepossesses no supply of emission substance or storage space therefor, butinstead is disposed at the end of an auxiliary discharge space as aworking electrode thereof for the attainment of its necessary heating bya cathodic bombardment. For this purpose, its retaining cylinders 2, ofthin sheet material, for example tantalum, may be connected through aninsulating piece 3 with the extended portion of a mounting enclosure 4,also of thin sheet material, for the accompanying auxiliary cathode 6,like Wise constructed as a capillary metal cathode, in particular withits porous carrier 5 for the emission substance. The arrangement is suchthat between the two carrier disks 1 and 5 for emission substance, asend members, a mechanically closed space is formed. However, in contrastto the above described arrangement, it will be apparent that the spacebetween the main cathode and auxiliary cathode also may be open, and inan extreme case, the main cathode may, in ultimate form, consist of aporous disk. Consequently, for example, the insulating intermediatepiece 3, instead of comprising a closed ring, may consist of individualpieces which bridge the space between the cylinders 2 and 4. The maincathode is activated in suflicient measure and maintained in operatingcondition by the emission-promoting substance. In addition, the appliedpotentials are so selected that the porous carrier disk 1 is loaded inthe manner of a draw anode, as working electrode by the electrons of theauxiliary discharge system accelerated toward it and its proper heatingduring operation is thus provided in such manner.

Advantageously, an additional metal layer may be applied to the porousdisk of the main cathode, which may, for example, be constructed oftungsten, to eifect a lowering of the temperature by means of areduction of the electron afiinity, said layer comprising metal selectedfrom the platinum group comprising platinum, cadmium and iridium.

Beside the small heat requirements of the main beam cathode, animportance advantage of the described electron beam production systemresides in the reduction of the danger of vaporization on the principalelectrodes, and in particular on insulating parts of the dischargevessel, with evaporating substances originating from the cathode, aswell as the possibility of an especially simple construction.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

I claim:

1. An electron production system for electronic discharge vessels, inparticular for power tubes, in the electron production system of which amain cathode is arranged as an operating electrode at the end of anauxiliary electron discharge space and heated by cathodic bombardment,comprising a main cathode constructed in the form of a dispenser cathodehaving a porous carrier disk from the front face of which the mainelectron beam is emitted, an auxiliary electron discharge space disposedbehind said porous carrier disk, an auxiliary electron discharge systemincluding an auxiliary cathode disposed in said space arranged todischarge electrons on the rear face of said main cathode, saidauxiliary cathode also being constructed in the form of a dispensercathode, operative to provide the emission-promoting substance for saidmain cathode which is received thereby as a basic part of such auxiliarycathode, said main cathode receiving its heater energy by cathodebombardment as an operating electrode of the auxiliary electrondischarge system.

2. An electron production system according to claim 1, wherein saidcathodes are individually supported by respective cylindrical members ofthin sheet material, said cylinders and cathodes being arranged to formsaid auxiliary electron discharge space with said cathodes beingdisposed at opposite ends thereof, and insulating means disposed betweenand connecting the respective cylinders.

3. An electron production system according to claim 2, wherein saidinsulating means is cooperable with the respective cylindrical membersand cathodes to form a closed discharge space. i

4. An electron production system according to claim 1, wherein means areprovided for supporting said main cathode in operative position withrespect to said auxiliary cathode, which means is so constructed thatsaid auxiliary electron discharge space is not completely closed and thepores of the porous carrier disk of the main cathode do not form thelargest openings in such space.

5. An electron production system according to claim 1, wherein thegeometrical arrangement and construction of the electrodes of the systemare such that with'predetermined operating potentials applied thereto,the cathodic bombardment eflects a predetermined uniform heating of theporous carrier disk of the main cathode.

6. An electron production system according to claim 1, wherein theporous carrier disk of the main cathode is constructed of tungsten andis provided with a layer of metal selected from the group consisting ofosmium, iridium and platinum, which layer forms the emission surface ofsuch cathode.

References Cited UNITED STATES PATENTS 2,830,917 4/1958 Kern 313-346 X2,843,785 7/1958 Iversen 313-346 X 2,953,701 9/1960 Gale 3l3346 X3,070,724 12/1962 Herbert et al. 313346 X 3,159,461 12/1964 MacNair 3l3346 X 3,348,092 10/1967 Beggs 313-346 JOHN W. HUCKERT, PrimaryExaminer R. F. POLISSACK, Assistant Examiner U.S. Cl. X.R. 313-338, 346

